Java中的基本数据类型转换
如果想要做ORM,将数据映射为对象,则基本的数据类型转换是必要的功能,而Java似乎未提供该功能,只有自己下手来完成该功能.
完成该功能的目标如下:
1: 提供基本的数据转换
2: 考虑转换的性能.
下面是我的具体实现:
1: 接口:
public static <T> T Cast(Class<T> t, Object value)
2: 依赖:需要依赖与获得数据默认值,因为在很多情况下,如果要转换的数据为null,调用者期望的是返回默认值.
系统自动提供的默认值不能满足我们的需求,例如int的默认值为0,但是在sql查询中,如果查询失败,我们期望的是小于0的值,例如Select Count(1) from table1这样的操作.
3: 实现:
/**
* 类型转换
* @param t
* @param value
* @return
*/
@SuppressWarnings("unchecked")
public static <T> T Cast(Class<T> t, Object value) {
if (value == null) {
return GetDefault(t);
}
if (t == Object.class) {
return (T)value;
}
try
{
return Cast_i(t, value);
} catch(Exception ex) {
ex.printStackTrace();
return GetDefault(t);
}
}
private static String GetStr(Class<?> t, Object value) {
if (value == null) {
return "";
}
if (t == String.class){
return (String)value;
}else {
return value.toString();
}
}
@SuppressWarnings("unchecked")
private static <T> T Cast_i(Class<T> t, Object value) {
Class<?> objClass = value.getClass();
if (t == String.class) {
return (T)GetStr(objClass, value);
}
if (t == int.class) {
if (objClass == int.class) {
return (T)value;
}
String text = GetStr(objClass, value);
Object ret = Integer.parseInt(text);
return (T)ret;
}
if (t == Integer.class) {
if (objClass == Integer.class) {
return (T)value;
}
if (objClass == int.class) {
return (T)value;
}
String text = GetStr(objClass, value);
Object ret = Integer.parseInt(text);
return (T)ret;
}
if (t == short.class) {
if (objClass == int.class) {
return (T)value;
}
String text = GetStr(objClass, value);
Object ret = Short.parseShort(text);
return (T)ret;
}
if (t == boolean.class || t == Boolean.class) {
if (objClass == int.class) {
Object ret = (int)value >= 1? true:false;
return (T)ret;
}
if (objClass == Integer.class) {
Object ret = (Integer)value >= 1? true:false;
return (T)ret;
}
String text = GetStr(objClass, value);
Object ret = Integer.parseInt(text);
ret = (int)ret >= 1? true:false;
return (T)ret;
}
if (t == long.class) {
if (objClass == long.class) {
return (T)value;
}
String text = GetStr(objClass, value);
Object ret = Long.parseLong(text);
return (T)ret;
}
if (t == byte.class) {
if (objClass == byte.class) {
return (T)value;
}
String text = GetStr(objClass, value);
Object ret = Byte.parseByte(text);
return (T)ret;
}
if (t == double.class) {
if (objClass == double.class) {
return (T)value;
}
String text = GetStr(objClass, value);
Object ret = Double.parseDouble(text);
return (T)ret;
}
if (t == float.class) {
if (objClass == float.class) {
return (T)value;
}
String text = GetStr(objClass, value);
Object ret = Float.parseFloat(text);
return (T)ret;
}
if (t == BigDecimal.class) {
if (objClass == BigDecimal.class) {
return (T)value;
}
String text = GetStr(objClass, value);
return (T)new BigDecimal(text);
}
if (t == java.util.Date.class){
if (objClass == java.util.Date.class) {
return (T)value;
}
String text = GetStr(objClass, value);
return (T)HiTypeHelper.Convert2Date(text);
}
if (t == java.sql.Date.class){
if (objClass == java.sql.Date.class) {
return (T)value;
}
String text = GetStr(objClass, value);
return (T)HiTypeHelper.Convert2SqlDate(text);
}
if (t == Time.class) {
if (objClass == Time.class) {
return (T)value;
}
String text = GetStr(objClass, value);
Object ret = HiTypeHelper.Convert2Date(text).getTime();
return (T)ret;
}
if (t == Timestamp.class) {
if (objClass == Timestamp.class) {
return (T)value;
}
String text = GetStr(objClass, value);
return (T)Timestamp.valueOf(text);
}
return (T)value;
}
3: 测试代码:
@Test
public void Test_HiTypeHelper_Cast() {
Integer val = 1;
int ret = HiTypeHelper.Cast(int.class, val);
Assert.assertEquals(ret, 1);
String text = "1";
ret = HiTypeHelper.Cast(int.class, text);
Assert.assertEquals(ret, 1);
text = "a";
ret = HiTypeHelper.Cast(int.class, text);
Assert.assertEquals(ret, -1);
int val2 = 1;
Integer ret2 = HiTypeHelper.Cast(Integer.class, val2);
Assert.assertEquals(ret2.intValue(), 1);
text = "1";
ret2 = HiTypeHelper.Cast(Integer.class, text);
Assert.assertEquals(ret2.intValue(), 1);
boolean bl = HiTypeHelper.Cast(boolean.class, 1);
Assert.assertTrue(bl);
bl = HiTypeHelper.Cast(boolean.class, 3);
Assert.assertTrue(bl);
bl = HiTypeHelper.Cast(boolean.class, 0);
Assert.assertFalse(bl);
bl = HiTypeHelper.Cast(boolean.class, -1);
Assert.assertFalse(bl);
bl = HiTypeHelper.Cast(boolean.class, "1");
Assert.assertTrue(bl);
bl = HiTypeHelper.Cast(boolean.class, "3");
Assert.assertTrue(bl);
bl = HiTypeHelper.Cast(boolean.class, "0");
Assert.assertFalse(bl);
bl = HiTypeHelper.Cast(boolean.class, "-1");
Assert.assertFalse(bl);
}
很多时候,数据转换在与数据库交互时使用较多,所以需要提供一些数据库类型的转换,主要是指时间或日期的转换.如:java.util.Date,java.sql.date与String和long之间的转换,下面是我的实现:
/**
* 字符串转换成日期
* @param text
* @return
*/
public static java.util.Date Convert2Date(String text) {
if (text == null || text.trim() == "") {
return null;
}
String format = "yyyy-MM-dd";
String str = text.trim();
if (str.contains(":")) {
format = "yyyy-MM-dd HH:mm:ss";
}
SimpleDateFormat sdf = new SimpleDateFormat(format);
try {
return sdf.parse(str);
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
return null;
}
}
/**
* 字符串转换为日期
* @param text
* @return
*/
public static java.sql.Date Convert2SqlDate(String text) {
java.util.Date dt = Convert2Date(text);
return new java.sql.Date(dt.getTime());
}
/**
* 日期转换为字符串
* @param date
* @return
*/
public static String ToShortString(java.util.Date date) {
if (date == null) {
return null;
}
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
return sdf.format(date);
}
/**
* 日期转换为字符串
* @param date
* @return
*/
public static String ToLongString(java.util.Date date) {
if (date == null) {
return null;
}
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
return sdf.format(date);
}
/**
* 日期转换为字符串
* @param date
* @return
*/
public static String ToShortString(java.sql.Date date) {
if (date == null) {
return null;
}
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
return sdf.format(date);
}
/**
* 日期转换为字符串
* @param date
* @return
*/
public static String ToLongString(java.sql.Date date) {
if (date == null) {
return null;
}
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
return sdf.format(date);
}
